Novel ablation-transfer imaging/recording

ABSTRACT

A unique method/system for simultaneously creating and transferring a contrasting pattern of intelligence on and from an ablation-transfer imaging medium to a receptor element in contiguous registration therewith is not dependent upon contrast imaging materials that must absorb the imaging radiation and is well adopted for such applications as, e.g., color proofing and printing, the security coding of various documents and the production of masks for the graphic arts and printed circuit industries; the ablation-transfer imaging medium, per se, comprises a support substrate and an imaging radiation-, preferably a laser radiation-ablative topcoat essentially coextensive therewith, such ablative topcoat having a non-imaging ablation sensitizer and an imaging amount of a non-ablation sensitizing contrast imaging material contained therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of and claims priority fromU.S. application Ser. No. 08/739,157, filed Oct. 30, 1996, which isprojected to issue on Mar. 25, 2003 as U.S. Pat. No. 6,537,720 and whichis a continuation of our now-abandoned application Ser. No. 08/525,039,filed Sep. 8, 1995, which is a continuation of our now-abandonedapplication Ser. No. 08/193,767, filed Feb. 9, 1994, which is acontinuation of our now-abandoned application Ser. No. 07/841,488, filedFeb. 26, 1992, which is both a continuation-in part of our now abandonedapplication Ser. No. 07/592,790, filed Oct. 4, 1990 and a division ofour application Ser. No. 07/706,775, filed May 29, 1991 and now U.S.Pat. No. 5,156,938, issued Oct. 20, 1992, which application Ser. No.07/706,775 is a continuation-in-part of our now-abandoned applicationSer. No. 07/497,648, filed Mar. 23, 1990, which is in turn acontinuation-in-part of our now-abandoned application Ser. No.07/330,497, filed Mar. 30, 1989. In U.S. Pat. No. 5,171,650, issued Dec.15, 1992 from the application of Ernest W. Ellis, et al., Ser. No.07/707,039, filed of even date with said application Ser. No.07/076,775, are disclosed and claimed a method-system of simultaneouslycreating and transferring a contrasting pattern of intelligence on andfrom a composite ablation-transfer imaging medium to a receptor elementin contiguous registration therewith, the composite ablation-transferimaging medium including at least one intermediate dynamic releaselayer, said application Ser. No. 07/707,039 being a continuation-in-partof commonly-assigned and now-abandoned application Ser. No. 07/592,790,filed Oct. 4, 1990.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to novel ablation-transfer imagingmedia comprising a support substrate having an imagingradiation-ablative topcoat essentially coextensive therewith, theimaging radiation-ablative topcoat including an ablation sensitizer andan imaging amount of a non-ablation sensitizing contrast imagingmaterial contained therein. This invention also relates to a transfermethod/system for simultaneously creating and transferring a contrastingpattern of intelligence on and from such ablation-transfer imaging mediato a receptor element in contiguous registration therewith, whereby saidimaging material delineates said pattern of intelligence thereon. Thepattern of intelligence transferred to the receptor element is thus ofopposite sign of that simultaneously created on the imaging medium.

[0004] The present invention especially relates to photo-inducedablation-transfer imaging/recording and, preferably, to laser-inducedablation-transfer imaging/recording particularly adopted for suchapplications as color printing/proofing and masking.

[0005] 2. Description of the Prior Art

[0006] The phenomenon of, e.g., laser-induced ablation-transfer imaging,is generically known to this art and is believed to entail both complexnon-equilibrium physical and chemical mechanisms. Indeed, suchlaser-induced ablation-transfer is thought to be effected by the rapidand transient accumulation of pressure beneath and/or within a masstransfer layer initiated by imagewise irradiation. Transient pressureaccumulation can be attributed to one or more of the following factors:rapid gas formation via chemical decomposition and/or rapid heating oftrapped gases, evaporation, photo and thermal expansion, ionizationand/or by propagation of a shockwave. The force produced by the releaseof such pressure is preferably sufficient to cause transfer of theimaging layer to an adjacent receptor element. The force is preferablysufficient to effect the complete transfer of the exposed area of anentire layer rather than the partial or selective transfer of componentsthereof.

[0007] Other material transfer imaging/recording techniques based onequilibrium physical changes in the material are also known to this art,but are limited in terms of both the overall speed of the process aswell as in the materials which can be employed therefor. In particular,ablation transfer differs from the known material transfer techniquessuch as, for example, thermal melt transfer and dye sublimation/dyediffusion thermal transfer (D2T2). Each of these prior art techniquestypically employs thermal print heads as the source of imaging energy.

[0008] Alternatively, it is known to employ laser heating in lieu of thethermal printing head. In these systems, the donor sheet includes amaterial which strongly absorbs at the wavelength of the laser emission.In the thermal melt transfer process, when the donor sheet isirradiated, this absorbing material converts the laser light to thermalenergy and transfers the heat to a colorant transfer layer which alsoincludes a binder, fusible compound, etc., thereby raising itstemperature above its melting point to effect its transfer onto anadjacent receptor sheet. In the D2T2 process, only the colorant istransferred to a specially treated or special receptor sheet (e.g.,coated or porous) by sublimation or thermal diffusion. See, for example,JP 62/140,884, UK Patent Application GB 2,083,726 and U.S. Pat. Nos.4,804,975, 4,804,977, 4,876,235, 4,753,923 and 4,912,083.

[0009] Compare also U.S. Pat. No. 3,745,586 relating to the use of laserenergy to selectively irradiate the uncoated surface of a thin filmelement, coated on one side with a contrast imaging absorber, tovaporize and to cause the selective transfer of the absorber coating toan adjacently spaced receptor, and U.S. Pat. No. 3,978,247 relating tosublimation transfer recording via laser energy (laser addressed D2T2),wherein the contrast imaging material is also the absorber.

[0010] Nonetheless, these processes are limited in a variety ofsignificant respects. For example, in melt transfer, the compositionmust contain low melting materials to transfer a pigment or dye andreceptor sheets appropriately textured for wicking or having specialcoatings are required for best results. In D2T2, only the imaging dyeitself is transferred; thus, it becomes necessary to employ specialreceptor sheets in order to effectively bind and stabilize (“trap”) thedye. Compare, for example, U.S. Pat. No. 4,914,078 to Hann et al.Furthermore, additional post-heating treatment steps, such as the“setting” of the dyes in the binder which is present on the receptorsheet increases both the complexity and the time associated with theprocess. Such process is also limited to those dyes and pigments whichundergo sublimation or diffusion in response to the particular imagingstimulus.

[0011] These processes are further limited in that the relatively slowprocesses of heat diffusion and thermal equilibrium are involved.

[0012] Accordingly, need exists in this art for a transfer process whichis far more rapid than current transfer techniques, which caneffectively employ a wide variety of contrast materials and which is notlimited to specially treated or special receptor elements.

[0013] Laser-induced recording based on the removal or displacement ofmaterial from the exposed area is also known to the recording art.However, these applications do not require transfer of material from onesubstrate to another. Historically, laser-induced recording has beenused, for example, in optical disk writing with near infrared (IR)lasers typically emitting at wavelengths ranging from 760 nm to 850 nmemployed as the writing source.

[0014] Since polymeric binders are typically non-absorbent in the nearinfrared region (760 nm to 2500 nm), infrared absorbers, i.e.,sensitizers, are added to the binders to absorb the laser radiation.This arrangement allows the laser radiation absorbed by the sensitizerto be converted to heat which causes pit formation. See, for example,U.S. Pat. Nos. 4,415,621, 4,446,233, 4,582,776 and 4,809,022 and N.Shimadzu et al, The Journal of Imaging Technology, Vol. 15, No. 1, pg.19 (1989). However, because this technology does not entail theimagewise transfer of materials from one substrate to another, thesesystems will not be further discussed.

[0015] There also exist in the recording art instances of laser-inducedablative transfer imaging entailing the displacement of material from adonor medium and adherently transferring same to an adjacent receptorelement. These are limited to the use of large amounts of a black bodyabsorber such as graphite or carbon black in conjunction with a Nd:YAGlaser emitting at 1064 nm to transfer a black image. See, for example,U.S. Pat. Nos. 4,245,003, 4,702,958 and 4,711,834 (graphitesensitizer/absorber), U.S. Pat. No. 4,588,674 (carbon blacksensitizer/absorber), and Great Britain Patent No. 2,176,018A (smallamounts of Cyasorb IR 165, 126 or 99 in combination with graphite as thesensitizer/absorber).

[0016] To produce these particular imaging media, thesensitizers/absorbers are usually dispersed in commercially availablebinders and coated onto a laser transparent support. The binders includeboth self-oxidizing binders, e.g., nitrocellulose, as well as non-selfoxidizing binders such as, for example, ethylcellulose, acrylic resins,polymethylmethacrylate, polystyrene, phenolic resins, polyvinylidenechloride, vinyl chloride/vinyl acetate copolymers, cellulosic esters andthe like. Since the black body absorbers employed are highly absorbentin the visible and ultraviolet (UV) as well as in the infrared region,the resulting transferred image is always black due to the presence ofthe absorber. Such ablative transfer imaging based on black bodyabsorbers is therefore entirely ineffective and wholly unsuited for manyapplications, e.g., color transfer imaging, color proofing, invisiblesecurity printing, etc.

[0017] Thus, serious need continues to exist in this art for aphoto-induced ablative transfer imaging medium that can be sensitizedindependently of the contrast imaging material(s) and is therefore notlimited to contrast materials which must absorb the imaging radiation.Like need exists for an ablative transfer imaging medium that may besensitized to absorb visible and/or near IR light.

[0018] In particular, existing desiderata in this art include:

[0019] 1. Media that can be employed in a photo-induced ablativetransfer process to provide full color images faster than possible usingcurrent melt or sublimation techniques and that can be tailored to meeta wide variety of specifications for color imaging.

[0020] 2. Media that can be employed in a photo-induced ablativetransfer process to produce masks which selectively block the light fromexposure units employed in pre-press production in the graphic arts andprinted circuit industries.

[0021] 3. Media that can be employed in a photo-induced ablativetransfer process to produce substantially colorless fluorescent images,e.g., for the security marking of documents.

SUMMARY OP THE INVENTION

[0022] Accordingly, a major object of the present invention is theprovision of novel technique for ablation-transfer imaging/recordingthat is not dependent upon contrast imaging materials that must absorbthe imaging radiation and which novel technique otherwise avoids orconspicuously ameliorates the above disadvantages and drawbacks to datecharacterizing the state of this art.

[0023] Another object of this invention is the provision of noveltechnique for ablation-transfer imaging/recording that is not dependentupon contrast imaging materials that must absorb the imaging radiationand which is well adopted, in contradistinction to the known state ofthe ablative recording art, for such applications asmulti-color/polychromal color proofing and color printing under a singleset of imaging conditions.

[0024] Briefly, the present invention features a method for transferringa contrasting pattern of intelligence from an ablation-transfer imagingmedium to a receptor element in contiguous registration therewith, saidablation-transfer imaging medium comprising a support substrate and animaging radiation-ablative topcoat essentially coextensive therewith,especially a photo- and more preferably a laser-ablative topcoat, saidessentially coextensive topcoat comprising an effectiveablative-transfer effecting amount of a non-imaging sensitizer thatabsorbs such imaging radiation, e.g., laser energy, at a rate sufficientto effect the imagewise ablation mass transfer of said topcoat, and saidimaging radiative-ablative topcoat including an imaging amount of anon-ablation sensitizing contrast imaging material contained therein. Inparticular, the present invention features a transfer method comprisingimagewise irradiating said ablation-transfer imaging medium according tosuch pattern of intelligence at a rate sufficient to effect the ablationmass transfer of the imagewise-exposed area of the radiation-ablativetopcoat of said imaging medium securedly onto said receptor element andwhereby said imaging material delineates said pattern of intelligencethereon.

[0025] This invention also features such ablation-transfer imagingmedium, per se, as well as an organization adopted for ablation-transferimaging/recording including such ablation-transfer imaging medium and areceptor element in contiguous registration therewith, e.g., inface-to-face registered direct contact, or even spaced a slight distancetherefrom which can extend up to 25 and in certain instances even up to100 microns.

[0026] The present invention also features an assembly forablation-transfer imaging/recording comprising the aforesaidorganization and means for selectively irradiating, e.g., with laserenergy or other sources of electromagnetic and even ultrasonicradiation, said ablation-transfer imaging medium to effect the ablationmass transfer of the selectively-irradiated area of theradiation-ablative topcoat of the imaging medium securedly onto thereceptor element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a side view photomicrograph of an imaging mediumaccording to the present invention and the illuminated space above same,100 nanoseconds after initiation of a 260 nanosecond laser pulsedirected through the support substrate of said imaging medium and intothe ablative topcoat thereof (the photomicrograph shows both the laserexposed and unexposed areas of the imaging medium);

[0028]FIG. 2 is a schematic/diagrammatic illustration of themethod/system according to the present invention, including oneembodiment of the imaging medium wherein the support substrate thereofis transparent to the imaging radiation; and

[0029]FIG. 3 is a schematic/diagrammatic illustration of anothermethod/system of this invention, including a second embodiment of theimaging medium wherein the support substrate thereof is not transparentto the imaging radiation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0030] More particularly according to the present invention, it will beappreciated that the imaging radiation-ablative topcoat necessarilycontains both a non-imaging ablation sensitizer that absorbs the imagingradiation as well as a non-ablation sensitizing contrast imagingmaterial.

[0031] It will thus be seen that the ablation-transfer imaging media ofthis invention provide the distinct advantage of being sensitizedindependently of the contrast imaging material, a feature conspicuouslyalien to the prior art.

[0032] By “ablation sensitizer” is intended any initiator capable ofinitiating and promoting the ablation process. It does this by absorbingthe imaging radiation and transferring the absorbed energy into anexplosive ablative force. Such sensitizers/initiators are well known tothe recording art. Light sensitization for imaging materials is ofcourse also well known to the recording art. However, in markedcontradistinction to the aforediscussed prior art laser-induced ablativetransfer imaging (wherein a material is also displaced from a donorsheet and adherently transferred to a receptor element to record apattern of intelligence thereon), the sensitizers of the presentinvention do not serve to distinguish or delineate the pattern ofintelligence. Their intended function is not reading.

[0033] For example, in color imaging applications, the sensitizer(s) ofthe invention is (are) substantially colorless. For security printingapplications where UV light is used to cause fluorescence of aninvisible pattern of intelligence, the sensitizer(s) of the inventiondoes (do) not fluoresce in the visible region. And for maskingapplications, e.g., for fabricating printed circuits or graphic artspreproduction, the sensitizer(s) of the invention does (do) not functionas the light blocking material.

[0034] Accordingly, such non-imaging ablation sensitizer is one thatabsorbs the radiation that causes ablation (write mode), but which isinvisible or not substantially discernible to the detector used todistinguish the resulting pattern of contrasting intelligence (readmode). The sensitizer may be invisible or not discernible because it isnonabsorbing or nonemitting to the detector, or because its absorbanceor emission is below the detection limit. Of course, the sensitizer mustbe capable of effecting the ablation of the topcoat under the intendedimaging conditions when employed without the non-ablation sensitizingcontrast imaging material.

[0035] By “non-ablation sensitizing contrast imaging material” isintended that material used to distinguish or delineate the resultingpattern of intelligence transferred to the receptor element.

[0036] Such contrast imaging material is, furthermore, incapable ofinitiating ablation-transfer without the above sensitizer/initiatorunder the intended imaging conditions that result in ablation. Failureof the contrast imaging material to itself initiate or promote ablationmay be the result of a lack of absorbance at the ablation wavelength(s),a lack of sufficient absorbance of same, or a failure of absorbance toresult in a pressure build up phenomenon, e.g., the absorbance providesa non-ablation promoting event such as photobleaching, stable triplet,fluorescence or phosphorescence. Thus, the contrast imaging materialmust be visible or discernible to the detector/technique used todistinguish the resulting pattern of intelligence transferred to thereceptor element and/or remaining on the imaging medium, per se.

[0037] Exemplary such contrast imaging materials that can be ablativelytransferred to a receptor element in a predetermined contrasting patternof intelligence to visibly or symbolically represent or describe anobject or data include the colorants (dyes or pigments), ultraviolet andinfrared absorbing materials, polymeric materials, magnetic materials,fluorescent materials, conducting materials, etc.

[0038] In a preferred embodiment of the present invention, the subjectablation-transfer imaging/recording technique is advantageouslyphoto-and more preferably laser-induced.

[0039] Photo- or laser-induced ablation-transfer comprehends a thresholdenergy below which no effective material transfer occurs and arequirement that the energy be input at a rate greater than the abilityof the materials to reverse the factors leading to the aforenotedpressure accumulation, for example by excessive thermal diffusionoutside the irradiated area. Thus, imaging radiation capable ofexceeding the threshold energy (fluence, joules/cm²) and power density(watts/cm²) is required for effective image transfer. By properselection of materials and imaging parameters, this latter requirementcan lead to exposure times on a nanosecond time scale which is at leastten times faster than exposure times necessary for conventional transferimaging processes. The actual values of fluence and power densitysuitable for photo- and laser-induced ablative transfer imaging aredependent on the specific materials employed in the imaging medium andthe specific receptor selected.

[0040] In a preferred embodiment of the invention, the imagingradiation-ablative topcoat comprises at least one sensitizer whichabsorbs at the wavelength of the desired laser output in the nearinfrared spectral region of 760 nm to 3,000 nm, and at least oneablative binder. The at least one sensitizer is present in an amountsufficient to effect the rapid partial decomposition of the at least onebinder when the at least one sensitizer interacts with laser light. Theablative binder advantageously comprises those polymeric materials whichundergo rapid acid catalyzed partial decomposition, preferably attemperatures less than 200° C. as measured under equilibrium conditions.The topcoat may also, optionally, contain materials which arenon-absorbing at the wavelength of the desired laser output and/ornon-decomposing, as well as optimal amounts of commercially availablebinders which are not ablative binders in the imaging process. Inanother preferred embodiment, as more fully discussed below, the topcoatcomprises at least one near infrared sensitizer, at least one ablativebinder, and at least one hydrogen atom donating material (H°) for theacid catalyzed decomposition of the ablative binder (which may bepresent in the binder itself).

[0041] In another preferred embodiment of the present invention, a nearinfrared laser-ablation transfer imaging medium is provided. Such mediumadvantageously comprises a near infrared transparent support filmbearing a layer of near infrared ablative coating employing asubstantially colorless near infrared sensitizer. This medium can beeffectively and advantageously employed for color imaging when a(non-sensitizing) colorant is added.

[0042] Upon exposure to laser light, the absorbing sensitizer interactswith the laser light and causes rapid partial decomposition of thebinder to gaseous and non-gaseous products. The rapid expansion of theheated gases causes ablation of the exposed topcoat onto an adjacentreceptor sheet providing a reverse of the imaged color film (i.e., acolor print or proof).

[0043] Suitable absorbing sensitizers according to the present inventioninclude any material which can absorb at a desired wavelength for aparticular near infrared or visible imaging wavelength and whichpreferably can initiate acid formation upon photo-excitation. Inparticular, where visibly transparent coatings are required, forexample, substituted aromatic diamine dication diradical typesensitizers or cation radical sensitizers with counterions derived fromstrong acids and absorbing in the near IR are preferred. Exemplary suchsensitizers include:

[0044] wherein R is alkyl, benzyl, substituted benzyl, etc.; X is SbF₆⁻, BF₄ ⁻, PF6″, AsF₆ ⁻, CIO₄ ⁻, B(phenyl)₄ ⁻, triflate and other saltsof strong acids which are not capable of electron donation to the cationradical or dication radical in the ground state; A is one of theradicals of the formulae:

[0045] and B is one of the radicals of the formulae:

[0046] in which Y is hydrogen, alkyl, aryl, nitro, halo, benzyl,substituted benzyl, etc.

[0047] Examples of these sensitizers include the series of near infraredabsorbers marketed under the trademarks Cyasorb IR 165, 126 and 99 byAmerican Cyanamid, as well as those IR absorbers described in U.S. Pat.No. 4,656,121, hereby expressly incorporated by reference.

[0048] Radiation sources emitting near infrared wavelengths incombination with visibly colorless sensitizers are preferred for highfidelity color imaging applications. In other applications, anyradiation source of sufficient intensity, typically not less than about10⁴ watts/cm², emitting in the visible and/or near infrared can beemployed for photo-ablation without limitation to black body sensitizersas essentially required by the prior art. The sensitizers of the presentinvention are most preferably highly absorbing at the wavelengths of theimaging radiation, soluble in the binders employed, and capable ofinitiating acid formation upon photo-excitation by the imagingradiation. Examples of suitable non-black body sensitizers which can beeffectively employed in the ablative topcoat are cyanine dyes,phthalocyanine dyes, metal dithiolenes, methylene blue salts, di- andtriarylmethane cation salts, Wurster's blue salts, and other visibly ornear infrared absorbing onium salts derived from strong acids, etc.Various of these are described in U.S. Pat. Nos. 4,315,983, 4,508,811,4,948,776, 4,948,777, 4,948,778 and 4,950,640, also hereby expresslyincorporated by reference.

[0049] Exemplary radiation emitting devices include solid state lasers,semiconductor diode lasers, gas lasers, xenon lamps, mercury arc lamps,and other visible and near infrared radiation sources which are capableof providing sufficient energy to equal, or exceed, the threshold energyfor ablation transfer and of providing this energy at such a rate as toinstitute that phenomenon of transient pressure accumulation discussedearlier and believed responsible for the ablative transfer process.

[0050] Since the value of threshold energy is intensity dependent, aswell as materials dependent it is desirable to provide this energy asrapidly as possible. Other constituents on the exposure device includethe ability to be focused to an image spot size and modulated at a dwelltime suitable for the desired application.

[0051] Particularly representative devices for providing the imagingradiation include lasers such as Nd:YAG lasers emitting at 1064 nm, forexample that incorporated in the imaging hardware of the CrosfieldDatrax 765 laser facsimile writer, laser diode systems emitting at780-840 nm, or other radiation sources designed to provide a powerdensity of 10⁴ watts/cm² or greater.

[0052] The radiation source is preferably focused to provide the mostefficient utilization of energy when it is impinged upon the imagingmedium.

[0053] The ablative binders according to the present invention areadvantageously those polymeric materials which transfer under theimaging conditions, and are preferably those which undergo rapid acidcatalyzed partial decomposition at temperatures of less than about 200°C. as measured under equilibrium conditions, and most preferably attemperatures of less than about 100° C. as measured under equilibriumconditions.

[0054] In particular, the preferred ablative binders according to thisinvention are those binders which decompose rapidly to produce effectiveamounts of gases and volatile fragments at temperatures of less thanabout 200° C. as measured under equilibrium conditions and thedecomposition temperatures of which are significantly reduced in thepresence of small amounts of generated acids. Most preferably, thedecomposition temperatures thereof are decreased to less than about 100°C.

[0055] Exemplary such polymers include nitrocellulose, polycarbonatesand other polymers of the type described in J. M. J. Frechet, F.Bouchard, F. M. Houlihan, B. Kryczke and E. Eichler, J. Imaging Science;30(2), pp. 59-64 (1986), and related polymers which are hereinafter morefully discussed.

[0056] Exemplary polycarbonate binders include those of the structure:

[0057] wherein B is one of the radicals of the formulae:

[0058] or other groups capable of generating a tertiary carbonium ionupon thermolysis and of producing gain or amplification in thedecomposition of the polymer by eliminating a proton from the carboniumion.

[0059] Stated differently, in addition to a thermal decomposition, asillustrated in the model system below:

[0060] the mechanism of the present invention preferably entails an acidcatalyzed thermal decomposition:

[0061] as generally described by J. M. J. Frechet et al, Journal ofImaging Science, 30(2), 59(1986). Commercially available Bisphenol Apolycarbonate decomposes at temperatures greater than 300° C.Non-tertiary diols and polyols may be polymerized in combination withtertiary diols to improve the physical properties of the polymer.

[0062] A may be the same as B or selected from among those dihydroxyaromatic or polyhydroxy compounds polymerizable into a polycarbonate.

[0063] The compounds:

[0064] are preferred.

[0065] The synthesis of these polymers has also been described, forexample, by J. M. J. Frechet et al, Polymer Journal, 19(1), pp. 31-49(1987).

[0066] In addition to the polycarbonates, polyurethanes having thefollowing general structure can also be employed:

[0067] wherein B is as defined above and A is selected from among thosearomatic or aliphatic diisocyanates or polyisocyanates copolymerizablewith the above tertiary diols to produce a polyurethane.

[0068] The compounds:

[0069] are the preferred.

[0070] It is known that polyurethanes of primary and secondary diols andpolyols decompose at temperatures greater than about 200° C. by theelimination mechanism:

[0071] wherein R is alkyl.

[0072] However, polyurethanes containing certain tertiary alcoholrecurring structural units can decompose at temperatures less than about200° C. by cleavage in a mechanism analogous to that of Frechet'spolycarbonates, as illustrated below:

[0073] In addition to the immediately aforesaid polycarbonates, thepolyurethanes that thermally decompose by acid catalysis are alsopreferred.

[0074] Small amounts (typically less than 10%) of non-tertiary diols andpolyols may be polymerized in combination with the tertiary diols toimprove the physical properties of such polymer without raising theenergy requirements for ablation-transfer imaging. The synthesis ofthese polyurethanes is described in Example 1 below.

[0075] Other than the polycarbonates and polyurethanes, polyesters ofthe following general formulae derived from malonic or oxalic acid mayalso be employed:

[0076] wherein B is as defined above. Polyorthoesters and polyacetalsmay also be used.

[0077] Typically, without raising the energy requirements forablation-transfer imaging, small amounts (e.g., less than about 10%) ofnon-tertiary diols and polyols may be polymerized in combination with Bto improve the physical properties of the polymer.

[0078] Small amounts (e.g., typically less than about 10%) of othercompatible di- and polyacids may be polymerized in combination with themalonic or oxalic acid to improve the physical properties of the polymerwithout raising the energy requirements for ablation-transfer imaging.

[0079] Alternating block copolymers containing polycarbonate,polyurethane and/or polyester recurring structural units as describedabove, as well as those including polyorthoester and polyacetalrecurring structural units, may also be used.

[0080] Other suitable ablative binder polymers include nitrocellulose,with a low viscosity SS (solvent soluble) nitrocellulose beingparticularly preferred from a coatability standpoint. Other examples ofnitrocellulose which can be employed are described at pages 329-336 ofCellulose and Its Derivatives by Ister and Flegien which is incorporatedherein by reference.

[0081] In addition, for proofing applications, the nitrocellulose ispreferably added in the form of nitrocellulose containing printing inkswhich are compatible with the solvent used to dissolve the sensitizer.Examples of such compositions include solvent based gravure inks andprocess printing inks.

[0082] As indicated above, the binder employed ideally is soluble in thesame solvent used for dissolving the near infrared absorbing sensitizer.However, dispersions may be used in appropriate circumstances when amutual solvent cannot be determined.

[0083] The coating composition may also contain other materials whichare non-absorbing at the desired laser emission wavelengths and/ornon-decomposing and do not adversely affect the absorbance of thetopcoat at the laser wavelength. These materials are selected dependingupon the function of the final product to be produced. These materialsmay play a role in the imaging chemistry or may be inert.

[0084] In a preferred embodiment, substances believed capable ofdenoting H (hydrogen atom) to the excited state of the sensitizer areincluded in the coating compositions, and may thereby increase acidformation. Such materials include alcohols, thiols, phenols, amines andhydrocarbons. Particularly preferred are low molecular weight secondaryand tertiary alcohols, diols and polyols such as 1,2-decanediol,pinacol, 2,5-dimethylhexane-2,5-diol, 2,5-dimethyl-3-hexyne-2,5-diol andcombinations of these. Addition of the hydrogen atom donors to thecoating surprisingly enables the reduction of the amount of near IRabsorber(s) from about 50% by weight based on solids content to about 5%to about 15% by weight based on solids content.

[0085] However, if, for example, nitrocellulose is employed as thepolymeric binder, the use of an additional hydrogen atom donor materialis not required because the desired hydrogen donors are already presentwithin the resin.

[0086] Other additives which may be included are selected dependent onthe final application of the imaged product. These additives arematerials which can be ablatively-transferred to a receptor element in apredetermined contrasting pattern of intelligence to visibly orsymbolically represent or describe an object or data, e.g., dyes andpigments, ultraviolet and infrared absorbing materials, polymericmaterials, magnetic materials, conducting materials, fluorescentmaterials, etc.

[0087] Still other additives may be included to enhance the filmproperties and transfer characteristics. These additives need notfunction as a contrast imaging material and include, e.g., plasticizers,flow additives, slip agents, light stabilizers, anti-static agents,surfactants, brighteners, anti-oxidants and others known to theformulation art.

[0088] In one embodiment of the invention, in which the imaging mediacan be effectively employed in color transfer printing, the contrastadditives are visibly absorbing dyes or pigments. The particular choiceis dictated by the specifications for the final colored print. Forexample, in a color proofing application suited to newspaper printing,American Newspaper Publishers' Association (ANPA) specified Color Index(C.I.) Pigment Blue 15, C.I. Pigment Yellow 13 and C.I. Red 57 are usedwith a newsprint receptor. For color imaging which need not conform toany industry specifications, visibly absorbing dyes such as thoseavailable in the Morfast™ series (Morton International) can be used withany desired receptor, e.g., office copy paper. By “color proofing” is ofcourse intended that technique, very well known to the recording art, ofpredicting or confirming one or more aspects of color printing prior topress, e.g., color rendition, tonal rendition, registration,composition, and the like.

[0089] In another embodiment, i.e., masking, in which the imaging mediacan be effectively employed as an exposure mask for use in graphic artsor printed circuit preproduction, the contrast additive comprises atleast one material, other than the black body absorbers known to theprior art, which is effective in blocking the light output from commonexposure devices. Exemplary such materials are curcumin, azoderivatives, oxadiazole derivatives, dicinnamalacetone derivatives,benzophenone derivatives, etc. By “masking” is intended that operation,also very well known to the recording art, including exposure of atypically light sensitive material, e.g., printing plate, resist, diazo,etc., through a pre-existing pattern of intelligence, e.g., a “mask”,which selectively blocks the exposure radiation according to the patternof intelligence, e.g., a printed circuit, newspaper page, etc.

[0090] In still another embodiment, in which the imaging media can beeffectively employed in a security printing application, the contrastadditives are substantially colorless materials which fluoresce in thevisible spectral region when exposed to ultraviolet light.Representative such materials include oxazole derivatives, oxadiazolederivatives, coumarin derivatives, carbostyryl derivatives, etc.

[0091] In yet another embodiment, the non-ablation sensitizing contrastimaging material is magnetic, for the production of such machinereadable items as information strips, checks, credit cards, etc.Exemplary thereof are iron, iron oxide, cobalt-iron oxide, bariumferrite, mixtures of the above, and the like.

[0092] The sensitizer and ablative binder are present in amountssufficient to allow rapid partial decomposition of the binder to gaseousand non-gaseous products when the sensitizer interacts with imagingradiation, e.g., laser light. Preferably, the ablative binder is presentin an amount of about 20% to about 95% by weight of dry solids while thesensitizer is present in an amount of about 5% to about 50% by weight ofdry solids. In addition, the additives can be present in an amount ofabout 0.5% to about 50% by weight of dry solids while the hydrogen atomdonor, including that provided by the polymer itself, can be present inan amount of about 1% to about 10% by weight of dry solids.

[0093] To prepare the coating composition for depositing the topcoataccording to the present invention, a solution or dispersion isformulated which contains solvent, the near infrared absorbingsensitizer, the ablative binder and, optionally, the hydrogen atom donorand/or additives. Preferably, the components of the wet coating arepresent in amounts of about 0.2% to about 5% by weight of the absorbingsensitizer, about 0.5% to about 20% by weight of the ablative binderand, optionally, about 0.5% to about 2% by weight of a hydrogen atomdonor and/or about 2% to about 20% by weight of the additives, with theremainder being solvent.

[0094] The dried coating is preferably less than three microns thick andmost preferably less than one micron thick in order to minimize theamount of energy required for ablative transfer. Furthermore, theimaging medium advantageously has an absorption of at least 0.1absorbance units at the wavelength(s) of the imaging radiation.

[0095] The solvent employed in the present invention includes thosesolvents which dissolve both the binders and preferably the near IRsensitizers. Exemplary such solvents include water, chlorinatedhydrocarbons, such as methylene chloride, 1,1,1-trichlorethane,chloroform, carbon tetrachloride, trichloromethane and the like; ketonessuch as acetone, methyl ethyl ketone, methyl propyl ketone and higherboiling analogs whose boiling points do not exceed the thermaldecomposition thresholds of the binder resin, or mixtures thereof.

[0096] After the solution or dispersion is formulated, it is coated ontothe support substrate by methods which are well-known to this art suchas Meyer rod coating, gravure coating, reverse roll coating, modifiedbead coating or extrusion coating.

[0097] The support substrates employed can be either support filmstransparent to the imaging radiation or non-transparent such supportfilms. Transparent support films which can be employed include glass,polyesters (by reason of their high optical clarity and dimensionalstability), polycarbonates, polyurethanes, polyolefins, polyamides,polysulfones, polystyrenes, cellulosics and any support substrate whichdoes not dissolve in the coating solvents employed, with polyestersbeing preferred. Examples of non-transparent supports include anynon-transparent support substrate which would not dissolve in thecoating solvents employed. These supports can include filled and/orcoated opaque polyesters, aluminum supports, such as used in printingplates, and silicon chips. The thickness of such support substrates isnot critical and can vary widely, same depending, for example, upon theparticular intended application and whether irradiated from the front orback surface thereof.

[0098] An anti-reflection layer (vis-à-vis the imaging radiation) mayoptionally be provided on the face surface of the support opposite theablative topcoat and/or on the receptor element, to enhance theefficiency of the ablative transfer by enabling more of the imagingradiation to be effectively utilized.

[0099] Such anti-reflection layer advantageously comprises one or morematerials which are recognized for this purpose in the recording art,for example those described in U.S. Pat. Nos. 3,793,022 and 4,769,306,and are also applied in known manner. Suitable materials, e.g., for apolyester support substrate having a refractive index of about 1.6, arecoatable materials having refractive indices of about 1.3 to 1.4.Exemplary such materials include Fluorad™ FC-721 from 3M Co., CaF₂,MgF₂, fluoropolymer, etc. The thickness of the anti-reflection layer(s)is selected as to provide the desired refractive properties for thelayer(s) with respect to the wavelengths of the imaging radiation. Forexample, where Fluorad™ FC-721 is employed as the anti-reflection layerand 1064 nm imaging radiation is used, a thickness of about 0.2 to 0.25microns is effective.

[0100] When the sensitizer is selected such as to be substantiallycolorless in the visible spectral region (400-760 nm), the laser imagingmaterials of the present invention can be advantageously employed in acolor imaging and proofing method. By this method, a receptor sheet ispositioned and firmly maintained, e.g., in a vacuum frame, relative tothe above described laser imaging material in such manner that it iseffective in receiving materials which have been ablated from theimaging medium.

[0101] The material transfer phenomenon of the laser-induced ablationprocess is illustrated by the photomicrograph obtained by time resolvedgrazing incident microscopy, TRGIM, in FIG. 1.

[0102]FIG. 1 is a side view photomicrograph of an imaging mediumaccording to the invention and the illuminated space thereabove (in lieuof a receptor element), taken 100 nanoseconds after the initiation of a260 nanosecond pulse from a Nd:YAG laser, 4, directed through thepolyester support, 3, about ¼″ from the edge thereof and into theabsorbing ablative topcoat, 2 (the imaging medium, per se, is more fullydescribed in the Example 6 which follows), to produce a plume, 5, ofablated materials. The horizontal lines, 1, in the space above themedium are interference lines resulting from the use of coherent probeillumination. The Nd:YAG laser (1064 nm output from a Quantronics1166FL-0 laser controlled by an Anderson Laboratories' DLM-40-IR2.7acousto-optic modulator and a 40 MHz signal processor) delivered 0.6J/cm² in a 25 micron diameter beam (1/e²). In FIG. 1, both the laserexposed and unexposed areas of the imaging medium are shown.

[0103]FIG. 2 illustrates the use of an imaging radiation transparentsupport substrate in the method of the present invention. In thisembodiment, imaging radiation 4 impinges upon the imaging material whichcomprises an imaging radiation transparent support substrate, 1, theablative topcoat, 2, and a receptor element, 3, from the back or supportside of said imaging medium.

[0104]FIG. 3 illustrates an alternative embodiment of the presentinvention wherein the imaging material comprises a nontransparentsupport substrate 5. In this embodiment, the receptor element, 3, ismade of imaging radiation transparent material and the imaging radiationimpinges upon the imaging material from the front or receiver sheet sideof the material.

[0105] In either embodiment, a pattern of imaging radiation at thedesired wavelength(s) is directed into the absorbing layer to effectrapid partial decomposition of the binder(s) to gaseous products, etc.,that gives rise to that phenomenon of temporary pressure accumulationdiscussed earlier. This causes ablation of the topcoat and its transferto the receptor element, thus producing an imaged donor film, 6, and acorresponding image of opposite sign on the receptor element, 7.

[0106] The receptor element need not be specially treated or selected toeffectively receive materials from the donor medium and can include, forexample, those which are well-known in the art of proofing and printing,such as newsprint, coated or uncoated papers of all shades and color,opaque filled and opaque coated plastic sheets, with the printing stockto be employed in the particular color proofing application beingpreferred. Other suitable receptors include fabrics, wood, cardboard,glass, ceramics, leather, metals such as aluminum and copper, rubber,papers and plastics generally, etc. While the receptor element need notbe specially treated or selected to assist in the ablation-transferprocess, as indicated above, it is nonetheless also within the scope ofthis invention to employ a treated or coated receptor, for example areceptor sheet coated with an effective amount of an adhesive or sizing,to aid in the adhesion of the ablated topcoat thereto.

[0107] The imaging medium is most advantageously positioned and firmlymaintained in face-to-face registered direct contact with the particularreceptor element selected, to facilely transfer ablated topcoat thereto,by any means suitable for such purpose, e.g., positive pressure, avacuum, or even by the adhesive properties of the receptor elementitself.

[0108] In order to further illustrate the present invention and theadvantages associated therewith, the following specific examples aregiven, it being understood that same are intended only as illustrativeand in nowise limitative.

EXAMPLE 1

[0109] Polyurethane Synthesis (Polymer VII from Table I):

[0110] 2,4-Toluene diisocyanate (TDI), 20 g,2,5-dimethyl-3-hexyne-2,5-diol, 16.3 g, dibutyltin dilaurate, 0.25 ml,and N-methyl pyrrolidone, 50 ml, were added to a 200 ml flask equippedwith a magnetic stirring bar and a nitrogen inlet. The solution wasstirred 6 hours at 50″C., then at room temperature overnight. Thepolymer was isolated by precipitation from water. It had a molecularweight of approximately 7,000 (GPC) and a thermal decompositiontemperature of 165° C. (broad) as determined by Differential ScanningCalorimetry (DSC) at a scan rate of 25″C./min.

[0111] The polyurethanes indicated by the Roman numerals V to XIII inTable 1 were synthesized from the corresponding monomers depicted in thefirst horizontal and vertical columns by the immediately aboveprocedure. The polycarbonates III and IV in Table 1 were synthesizedfrom the corresponding monomers depicted, after appropriatederivatization of the diols as described in J. M. J. Frechet et al,Polymer Journal, 19(1), pp. 31-49 (1987): TABLE 1

V VI III

VII VIII IV

IX X

XI XII

[0112] The above polymers were evaluated by DSC. The results reported inTable 2 were obtained: TABLE 2 Softening/ Melt Temp. Decomposition Temp.Polymer (° C.) Melt Energy (J/g) (° C.) III 139 22 180 IV 50 21 170 V —— 200 VI — — 110 VII 46 85 165 VIII 100 — 113 IX — — 157 X 63 — 100 XI94 22 206 XII 50 100 174 Ethylcellulose 96 17 203 Polyacetal — — 171

EXAMPLE 2

[0113] The following solution was coated onto ICI Melinex 516 polyesterfilm, 12″×18″ and 4 mils thick, with a #4 Meyer rod at a loading of 0.5g wet weight/ft². Addition of the components was in the order indicated:7.25 g Acetone 1.197 g  Copolymer of 1,4-TDI &2,5-dimethyl-3-hexyne-2,5-dio (Polymer VII from Table 1) 0.364 g Cyasorb IR 165 0.12 g 2,5-Dimethyl-3-hexyne2,5-diol 1.06 g MorfastYellow 101.

[0114] The yellow film thus produced was imaged in registration with anewsprint receptor using a yellow halftone separation film master on aCrosfield Datrax 765 Facsimile system which employed a Nd:YAG laser withoutput wavelength 1064 nm and an adjustable power output of 3-14 Wattsat the film plane. The Datrax 765 writer is commercial hardwareavailable from Crosfield Electronics Ltd., Milton Keynes, UK. Theimaging conditions for this experiment were adjusted to an output powerof 10 Watts which gave a fluence of 0.16 J/cm², an intensity of 2×10⁶Watts/cm² and an addressability of 1,000 lpi at a 1/e² spot diameter of25 microns. The yellow film was maintained in direct contact with thenewspaper receptor via vacuum hold down at a pressure of 20 inches Hg.An imaged yellow film (negative) and a registered yellow newsprint image(positive) were produced at a scan rate of 64 cm²/sec.

EXAMPLE 3

[0115] To make a two color print, the solution of Example 2 wasprepared, but substituting a combination of Morfast Red 104, 0.76 g, andMorfast Violet 1001, 0.04 g, in place of the Morfast Yellow. The magentafilm thus produced was imaged as described in Example 2 using magentahalftone separation data with the yellow print from Example 2 as thereceptor sheet. A two color print (positive) and an imaged magenta film(negative) were produced.

EXAMPLE 4

[0116] To make a three color print, the solution of Example 2 wasprepared, but substituting a combination of Morfast Blue 105, 0.4 g, andMorfast Blue 100, 0.4 g, in place of the Morfast Yellow. The cyan filmthus produced was imaged as described in Example 2 using cyan halftoneseparation data with the two color print from Example 3 as the receptorsheet. A three color print (positive) and an imaged cyan film (negative)were produced.

EXAMPLE 5

[0117] To make a four color print, the solution of Example 2 wasprepared, but substituting a combination of Morfast Brown 100, 0.35 g,Morfast Blue 105, 0.36 g, and Morfast Red, 0.36 g, in place of theMorfast Yellow. The neutral black film thus produced was imaged asdescribed in Example 2 using black halftone separation data with thethree color print from Example 4 as the receptor sheet. A four colorprint (positive) and an imaged black film (negative) were produced.

EXAMPLE 6

[0118] The following formulation was coated as described in Examples 2through 5:  7.25 g Acetone 0.364 g Cyasorb IR 165  2.5 g American Ink &Coatings Co. gravure inks Process Yellow or Process Red or Process Blueor Process Black.

[0119] The American Ink gravure inks included nitrocellulose. Films wereimaged as described in Examples 2 through 5 to produce full color printswhich meet ANPA specified solid ink hue and density on newsprint: cyan,0.90-0.95, magenta, 0.90-0.95, yellow, 0.85-0.90, black, 1.00-1.05.

EXAMPLE 7

[0120] The following solution was formulated and coated as described inExamples 2 through 5:  7.25 g Acetone 1.197 g Copolymer of 4,4′-diphenylmethane diisocyanate and PARADIOL (trademark of Goodyear Chemicals)(Polymer X from Table 1) 0.364 g Cyasorb IR 165  0.12 g2,5-Dimethyl-3-hexyne-2,5-diol  2.5 g American Ink & Coatings Co.gravure inks Process Yellow or Process Red or Process Blue or ProcessBlack.

[0121] Films were imaged as described in Examples 2 through 5 to producefull color prints, as well as individual imaged monocolor and blackfilms.

EXAMPLE 8

[0122] To 8.35 g of a 50:50 mixture of 1,1,1-trichloroethane andmethylene chloride were added 0.5 g of an alternating polycarbonatesynthesized from Bisphenol A and 2,5-dimethylhexane-2,5-diol (PolymerIII from Table 1); 0.1 g Cyasorb IR 165; 0.1 g2,5-dimethyl-3-hexyne-2,5-diol; and 1.0 g of any one of the Morfastcolors described above. The solutions were coated at a loading of 1 g ofsolution/sq. ft. with a #9 Meyer rod by hand drawdown. The dried filmswere imaged at 0.11 J/cm² versus the 0.16 J/cm² in Example 2 on aCrosfield Datrax 765 to produce a color print on a receptor sheet andimaged monocolor or black films.

EXAMPLE 9

[0123] To 9.35 g of a 50:50 mixture of 1,1,1-trichloroethane andmethylene chloride were added 0.5 g of an alternating polycarbonateprepared from Bisphenol A and 2,5-dimethyl-3-hexyne-2,5-diol (Polymer IVfrom Table i); 0.1 g Cyasorb IR 165; and 0.05 g of2,5-dimethyl-3-hexyne-2,5-diol. The solution was coated on polyesterfilm and imaged at 0.08 J/cm2 versus the 0.11 J/cm² in Example 8 asdescribed above to produce an imaged light tan film and a reversal lighttan image on a newsprint receptor sheet.

[0124] By comparison, films prepared from bisphenol A polycarbonates,polyvinylidene chloride (Saran F120 or F300), polymethacrylonitrile,ethylcellulose N-7, or styrene/acrylonitrile copolymer am binders inplace of an ablative polycarbonate or polyurethane provided very littleor no image transfer to the receptor sheet at the imaging fluenceemployed in this example.

[0125] While this invention has been described in terms of variouspreferred embodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims including equivalents thereof.

What is claimed:
 1. A method for transferring a contrasting pattern ofintelligence from an ablation-transfer imaging medium to a receptorelement, said ablation-transfer imaging medium comprising a supportsubstrate and an imaging radiation-ablative topcoat, said topcoatcomprising a non-imaging sensitizer that absorbs imaging radiation at arate sufficient to effect the imagewise ablation mass transfer of saidtopcoat and an imaging amount of a non-ablation sensitizing contrastimaging material, which method comprises imagewise irradiating saidablation-transfer imaging medium according to such pattern ofintelligence at a rate sufficient to effect the ablation mass transferof the imagewise-exposed area of said topcoat securedly onto saidreceptor element and whereby said imaging material delineates saidpattern of intelligence thereon.
 2. A method for transferring acontrasting pattern of intelligence from an ablation-transfer imagingmedium to a receptor substrate, said ablation-transfer imaging mediumcomprising a support substrate and a laser radiation-ablative topcoat,said topcoat comprising a non-imaging sensitizer that absorbs laserradiation at a rate sufficient to effect the imagewise ablation masstransfer of said topcoat, and said topcoat including an imaging amountof a non-ablation sensitizing contrast imaging material, which methodcomprises imagewise laser-irradiating said ablation-transfer imagingmedium according to such pattern of intelligence at a rate sufficient toeffect the ablation mass transfer of the imagewise-exposed area of saidtopcoat securedly onto said receptor element and whereby said imagingmaterial delineates said pattern of intelligence thereon.
 3. The methodas defined by claim 2, wherein said topcoat comprises at least onelaser-ablative binder.
 4. The method as defined by claim 3, wherein saidtopcoat comprises at least one laser absorber/sensitizer.
 5. The methodas defined by claim 4, wherein said at least one laserabsorber/sensitizer comprises at least one near infraredabsorber/sensitizer.
 6. The method as defined by claim 5, wherein saidat least one laser-ablative binder is decomposable by acid catalysis. 7.The method as defined by claim 6, said topcoat further comprising atleast one hydrogen atom donor for promoting acid formation for saidcatalyzed decomposition.
 8. The method as defined by claim 5, saidsupport substrate being transparent to near infrared laser irradiation.9. The method as defined by claim 5, said support substrate being opaqueto near infrared laser irradiation.
 10. An ablation-transfer imagingmedium comprising a support substrate and an imaging radiation-ablativetopcoat, said topcoat comprising a non-imaging sensitizer that absorbssuch imaging radiation at a rate sufficient to effect the imagewiseablation mass transfer of said topcoat, and said topcoat including animaging amount of a non-ablation sensitizing contrast imaging material.